Thomas M. Siebel Chair in the History of Science at University of Illinois-Urbana Champaign
Maxwell’s Demon

Carl Sagan spoke too soon when he spoke about demons. Modern science, he told his numerous followers, banished witches, demons and other such creatures from this world. Simply spread flour on the floor and check for suspicious footprints—this kind of reasoning, he claimed in The Demon-Haunted World, characterizes sound, scientific thinking.

So why is Maxwell’s demon still on the frontlines of science? Since he was first conjured in 1874, modern day inquisitors have valiantly chased after him with math and physics instead of holy water. But rather than going the way of the phlogiston and the ether, he has emerged unscathed and is now a fixture in standard physics textbooks. Lest you think he is real, let me tell you he is not. But a demon he is in spades. He sorts, and sorting is at the origin of sorcery.

Neat-fingered and vigilant, he can reverse time, momentarily violate the second law of thermodynamics, power a perpetual motion machine, and generate pockets of hellish heat in substances that should otherwise reach temperature equilibrium. His smarts are debatable, matching those of a virtuoso piano player or those of a humble switchman on railway tracks. No offense is taken if he is compared to a simple valve. On the contrary, it means he can do a lot of work with minimum effort. Frequently portrayed as holding a cricket bat (to send molecules to-and-fro), manning a trapdoor (to let them pass or keep them out) and holding a torch, a flashlight or a photocell (to be able to see in the dark), this miniscule leviathan can wreak havoc.           

He was named after the Scottish scientist James-Clerk Maxwell, known for his theory of electromagnetism, by his colleague William Thomson (aka Lord Kelvin). Almost immediately after his public debut, he was exorcized. Sightings of his demonic activity were brushed away as statistical anomalies or insignificantly tiny—no need to worry, we were told.          

But science can, and often does, turn imaginary beings into real things. Maxwell’s demon is a case in point. Since he was first conjured, scientists have tried to bring him to life repurposing twisted metal, ratchets and gears, molecules, enzymes and cells, and even electronics and software. In 1929 the physicist Leo Szilard published a paper about him in the prestigious Annalen der Physik (which reached fame as “Szilard’s exorcism”) before pairing up with Einstein to patent a refrigerator that would momentarily and locally reverse entropy. Another milestone took place in 2007, when an article in Nature titled “A Demon of a Device” described some of the first successful molecular nanomotors. At that time, Sir Fraser Stoddart considered it as auguring an entirely new approach to chemistry; he went on to win the Nobel Prize for Chemistry in 2016. Artificial intelligence is another technology with a connection to Maxwell’s being.

Maxwell’s demon is neither the first nor the last, but he is certainly the most well known of all science’s demons. Descartes’s demon preceded him by more than two centuries. Like a master illusionist who can take over your sense of reality by throwing a cloak over your head, this genie can intercept your sense-impressions and take over from there. He remains the patron saint of virtual reality. Laplace’s demon comes next: the master calculator who can relate every particle to the laws of motion and who can know the past and the future has inspired advances in supercomputing and Big Data. The so-called “colleague of Maxwell’s demon,” appeared a few decades after the original one. His arriviste career included travelling faster than light and helping to explain quantum entanglement. By sharing with biblical shedim the power of instantaneous locomotion, he can intercept messages, mess with causality, and fiddle with time. These shape-shifting masters of disguise are getting smarter and more powerful. By taking on the name of the scientists who conjured them, they dutifully fulfill their patronymic destiny, reappearing regularly as spick-and-span newborns with the sagacity of old men.

At the turn of the nineteenth century the French mathematician Henri Poincaré claimed he could almost see Maxwell’s demon through his microscope, calculating that with a little patience (of millions of millions of centuries) his mischief would be evident for everyone.  While some deemed him too small to really matter for us, others noted that small causes were known to produce great effects, like the spark or the pebble starting an avalanche. Other scientists argued that the universe as a whole was so large that he could confidently reign like a master in a confined territory. For Norbert Wiener, founder of cybernetics, it was clear that “there is no reason to suppose that metastable demons do not in fact exist.” The physicist Richard Feynman wrote an entire article explaining why, when and how he would eventually tire. According to Isaac Asimov, everything that appeared to us as if arriving by chance was really because “it is a drunken Maxwell’s demon we are dealing with.”

It is perhaps most ironic that the philosopher Sir Karl Popper, known for describing the process of scientific progress as one based on hypothesis-creation and falsification, admired his ability to survive every assassination attempt against him: “Although innumerable attempts have been made on his life, almost from the day he was born, and although his non-existence has frequently been proved, he will no doubt soon celebrate his hundredth birthday in perfect health and vigor.”

Demons are here to stay. The reassuring predictions of scientists such as Carl Sagan have proved to be overly premature. In our hurry to make our world modern and base it on purely secular reason, we have failed to see the demons in our midst.